The invention relates to a thermostatic device of the electric-motor-actuated valve type comprising a thermostatic element which may be a conventional expanding-wax thermostatic element so that it also has a backup mode of operation in the event of failure of the motor or of its control equipment.
Thermostatic devices of the valve type are used in particular in internal combustion engine cooling circuits to regulate the temperature of the cooling liquid introduced into this engine to optimize its operation, by influencing the flowrate of so-called xe2x80x9ccoldxe2x80x9d liquid from the vehicle radiator and/or the flowrate of so-called xe2x80x9chotxe2x80x9d liquid from the engine, which are mixed to form a so-called xe2x80x9cwarmxe2x80x9d cooling liquid which is reintroduced into the engine. Note that the terms xe2x80x9ccoldxe2x80x9d, xe2x80x9chotxe2x80x9d, and xe2x80x9cwarmxe2x80x9d are used with a view to simplifying the vocabulary used to indicate the relative temperature levels of the three streams of liquid when the device is operating in the steady state, but that in fact the respective temperatures of these three streams may be very similar, and are identical when the engine has been stopped for some time.
Thermostatic devices motorized by means of an electric motor comprising a backup thermostatic element allowing, for example, a stream of cold liquid to be mixed in a chamber of the device with the stream of hot liquid even when the motor or its control equipment fail, if the temperature of the liquid in which the thermostatic element is immersed exceeds a desired value, are already known, particularly from French patent published under the number 2 703 730.
The thermostatic device in this document 2 703 730 is motorized by means of an electric motor comprising a rotary output shaft which, by means of a conventional screw-nut coupling system converting the rotary movement of the shaft into a translational movement, actuates the moving plug of the thermostatic device, namely a spool, which gradually uncovers a cold liquid inlet access of this device at the same time as gradually plugging a hot liquid inlet access, and vice versa; the backup thermostatic element is aligned with the screw of the screw-nut system and when its temperature rises, its piston exerts on the spool, if the latter has not been moved or has been insufficiently moved, via the screw-nut system, a force directed in the direction for uncovering the cold liquid inlet access and plugging the hot liquid inlet access; so that under the thrust of the piston of the thermostatic element, the spool can actually move in this direction, the screw-nut system coupling is telescopic and, more specifically, mounted so that it can slide on the shaft of the motor while being urged toward the spool by a spring in the direction for uncovering the hot liquid inlet access and plugging the cold liquid inlet access; hence, when the thermostatic element exerts on the spool a force in the opposite direction which exceeds the spring force, to plug the hot liquid inlet access and uncover the cold liquid inlet access, the spring is compressed by the retraction of the screw-nut system and so nothing opposes these respective plugging and uncovering movements. A drawback with this device is that when the temperature of the liquid in which the thermostatic element is immersed drops, the screw-nut system accompanies the retracting movement of the thermostatic element which, because the electric motor or its control equipment has failed, leads to a further temperature rise, a further elongation of the thermostatic element, and operation which tends towards the unstable with a xe2x80x9cwarmxe2x80x9d liquid at a temperature higher than the normal temperature. Furthermore, the thermostatic element has to be relatively powerful in order to overcome the resistive force of the spring, and the screw-nut system with its telescopic spring-loaded mounting is relatively bulky, which means that the dimensions of the thermostatic device cannot be reduced as much as might be desired.
The object of the invention is to overcome these drawbacks and the invention therefore relates to a thermostatic device comprising a housing which has a chamber comprising at least two fluid accesses, at least one of which can be plugged by a plug, a motor fixed to the housing and equipped with an output shaft that is able to move in terms of rotation and with reversible direction of rotation, connected mechanically to the plug by a coupling involving a screw-nut system designed to actuate this plug in terms of translation, selectively, in a direction in which it gradually plugs the pluggable access and in a direction in which it gradually uncovers it according to the temperature of a stream of fluid travelling through the device and detected by a sensor, and a backup thermostatic element located at least partially in the same stream of fluid and comprising a moving part designed to actuate the plug in terms of translation when, as the result of a failure, this plug has not been actuated by the screw-nut coupling system and the temperature of the said stream of fluid exceeds by a predetermined value the temperature that should have caused such actuation by the screw-nut system, characterized in that the motor is of a type which, at rest, presents a resistive torque so as to allow a set position to be maintained, the coupling involving a screw-nut system is substantially inelastic and the screw-nut system is reversible so that if the plug is actuated in terms of translation by the moving part of the thermostatic element, the translational movement is transmitted by the plug to. the screw-nut system and causes the motor to rotate.
Owing to the reversibility of the screw-nut system and of the direction of rotation of the motor and to the translational inelasticity of the coupling, movements of the plug by the thermostatic element encounter only a low resistive force, and retraction of the thermostatic element does not cause elastic return of the plug to its initial position.
The thermostatic device may furthermore exhibit one or more of the following features:
the motor is an electric motor of a type which is electrically powered at rest so that it presents a resistive torque that is appreciably higher than the torque due to friction, for example a stepping motor or a motor with no commutator otherwise known as a brushless motor,
the motor is a stepping motor equipped with position-encoding means,
the predetermined value is about 5xc2x0 C.,
it comprises a housing and a base fixed together, the base comprising a pipe into which there opens an access of the chamber which is not pluggable and in which a sensor and a fixed part of the thermostatic element are at least partially situated,
the chamber comprises two accesses that can be plugged by a plug consisting of a spool actuated selectively in a direction in which it gradually plugs one of the accesses while gradually uncovering the other, and vice versa,
it further comprises two accesses which cannot be plugged by the plug and which are constantly in communication,
the chamber comprises two accesses, one of which can be plugged by a plug consisting of a shutter actuated selectively in a direction in which it gradually plugs, one of the accesses and vice versa,
it comprises a housing and a base fixed together, the base comprising a pipe into which there opens an access of the chamber which is not pluggable and into the side wall of which there opens an additional access which is also not pluggable,
the thermostatic element comprises a cup to which a bypass sealing shutter is secured, and the base internally comprises a chamber into which there opens a bypass access and which is connected to the internal region of the pipe by a seat for the bypass sealing shutter which is in the widest-open position when the plug is in the closed position and in the closed position when the sensor detects a very high temperature.